Apparatus for obtaining nitrogen dioxide from nitrous oxide



A. P. SABOL 2,974,019 APPARATUS FOR OBTAINING NITROGEN DIOXIDE FROM NITROUS OXIDE March 7, 1961 Original Filed. March 19, 1957 M mm .9 mm m INVENTOR I? .SABOL ALEXANDER ATTORNEY contained gas.

APPARATUS FOR OBTAINING NITROGEN DIOXIDE FROM NITROUS OXIDE Alexander 1. Sabol, Queens Lake, Rte. 2, Williamsburg, Va.

Original application Mar. 19, 1957, Ser. No. 647,168. Divided and this application July 23, 1958, Ser. No. 750,543

2 Claims. (Cl. 23-484) (Granted under Title 35, US Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method and apparatus for obtaining nitrogen dioxide from nitrous oxide by selfsustaining thermal decomposition of the nitrous oxide, and is a division of my co-pending application Serial No. 647,168 filed March 19, 1957, which is in turn a continuation-in-part of my copending application Serial No. 466,464, filed November 2, 1954, now Patent No. 2,799,- 159.

Heretofore, nitrogen dioxide has been obtained,con-

tinuously from nitrous oxide by passing the nitrous oxide through a straight tube heated from the outside toa temperature suflicient to bring about decomposition of the the necessity of maintaining external heat application on the tube, due to the fact that without the external heater the continuous entry of cool nitrous oxide extinguishes the reaction. v

Generally stated, this invention consists in amethod for obtaining a continuous and self-sustainingthermal breakdown of nitrous oxide with production of nitrogen dioxide. 7 v l i Y The primary object of the invention, therefore, isto provide a self-sustaining method for production of nitrogen dioxide from nitrous oxide. An object,-al so, is to provide a thermal decomposition method involving use of regenerative procedure tomaintain operative efficiency. Another object is to provideapparatus for etlective use of the method procedure. An additional object is to provide efiective control of the cooling of decomposition products of nitrous oxide so thatthe percentage of ob tained nitrogen dioxide may be modifie e Other objects and many of the attendant advantages of this invention will be readily appreciated as the'same becomes ,better understood-by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 1

Fig. Us a view of an elevation ofthe regenerative type reactor, with parts in section;

Fig. 2 is a View similarto Fig. 1, but showing modified cooling apparatusfor'the derived gases; and

Fig. 3 islia View, with parts in section, of a modified apparatus of the straight-flow type. .7 Recently published, reports indicatethat the manufacture of nitrogen dioxide (N0 which is a basic ingredient for nitric acid, appears. to be economically feasible through direct use ofatomic energy. In this process, however, largequantities of nitrous oxide (N20) are no large scale use;

A disadvantage of this prior method is.

addition to the elemental gases N and O and in the figures of the drawing, apparatus effective for'obtaining this decomposition is shown. I

In Fig. 1 there is illustrated the regenerative type reactor 10 provided with gas cooling equipment 11 added to control the quantity of N0 produced. This figure shows an outer tube 12 made from a refractory material with low heat-conductance, for example, a ceramic such as Vycor. One end 13 of this tube is closed, except for a central opening through which a pipe 14 of smaller diameter extends for about three-fourths the outer tube length. This inner tube 14, which is also of Vycor or the like, has an open inner end 15 and at its outer end 16, external to tube end 13, it is contracted to engage a supply pipe 17 provided with control'valve 18, the pipe having connection to the pressurized supply of N 0. Inner tube 14, for about a half of its length inside tube 12, has a reduced outside diameter and on this reduced section a layer 9 is applied of a material possessing high refractory property, high-thermal conductivity and resistance to spalling and oxidation, such as the commercial substance Carbofrax containing 85 percentor more of silicon carbide. a I

The end of tube 12 opposite to closed end 13,is open,

and closely seated in this open end and completely closing the opening is a stopper 20 made of ceramic or asbestos board, the edge of the stopper bearing an outer annular flange 21 seating snugly against the open end of outer tube 1 2. The stopper 20 has pronouncedthickness', so as to augment its use as a heat reservoir, and inner surface 22 is preferably roughened 'toqfenha'nce its use as a flame holder as will be described more fully j I hereinafter, V V

c The outer side of theouter tube 12, for about one-half its length, adjacent the stopper, is covered 'by 'a'layer {2 2 of heat andelectricity insulating material such as asbestos Q tape and over this tape "is wrapped a coil of electrical resistance wire 23, having'terminals 24', for heating the tube. Over the wire coil a second layer 25 of insulation material is placed, and over this second insulation layer" a sheet of heat conducting material 26 such as aluminum foil, is wrapped.

Adjacentthe inner closed end'13 of tube12, anop ening 27 is formed having, a threaded edge adapted to made for this purpose, opening '30, as closed by pm 'sr which fits both openings, being indicated. I

A cooling system 11 is provid d to control the rate of cooling of the gas moving through outlet nozzle 2h. i

system basically includes a gas expansion chamberSZ, a

water tank'33 adapted tohold water 34, a pipeline 3'5] from the chamber 33 to thetank 33 and a long nozz'le 36 attached to pipeline 35 and extending'approximately I along the entire length. of and within the tank 33,""adja- .jcentqthebase thereof. Nozzle 36 isiprovided.with'spaced 1 perforations 37 in the nozzle ;wall toipermit' gasilemand; V v tions at multiple points withinthe water of the tank '7 I The operation of the apparatus'willnow be explained.

produced as a byproduct for which there appears to be :11

In my experimental] Work pertaining to the continuous A internal heating of air in a hypersonic. wind tunnel" by decomposition of nitrous; oxide, as explained in i'copending, application .hereinab'ove greferredeto, .it' was dis-. I

Heating current is' first applied to the terminals 240i heater coil 23, whereby the decompositionchamber in he stopper 2i), jandindicated by .numeral33, is heatedtoa point where. the tube iZ'at tains a bright red color. vN 0, at' pressures which may vary from atmospherid'to abcut 37 V atmospheres, butwhich. have been found particularly efie'ctive atarou'n d: 25 atmospheres, is. then" introduced tube '12,.from; about one-half .thectube length K through "pipe 17 under control of valve 1 18, 'this' gas' pass- Patented Mar. 7, 1961 ing through inner tube 14 and after emergence at open end 15 in the decomposition chamber 38, impinging on the stopper surface 22, where the flow is reversed, the gas being forced against the heated wall of tube 12. As a result of this wall impact, the N decomposes and liberates its heat of formation, the resulting pressure increase and turbulence carrying gases to surface which is thus heated to a temperature sutficient to initiate decomposition of the inflowing N 0 striking this surface. As soon as this temperature condition of stopper surface 10 is reached, the current is cut off from heater 23 and the process becomes self-sustaining. After leaving decomposition space 38, the heated decomposed gases move reversely in the annular space between tubes 12 and 14 to the outlet nozzle 29, this reverse movement heating inner tube 14 and, thereby, the incoming N 0 gas.

The decomposition gases ejected from nozzle 29 include N0 N 0 and undecomposed N 0. These gases are now cooled and N0 is recovered by bubbling the gases through water, N0 only being absorbed by the water to form nitric acid.

It has been found that the rate of exhaust gas cooling is an important factor in determining the percentage of N0 recovery, a rapid rate being usually desirable. Cooling control, in the apparatus arrangement of Fig. l, is secured by the shape of outlet nozzle 29, the degree of contraction of the nozzle outlet being determining, by the point of placement of the nozzle along the tube 12, as at 27 or 30, for example, by the use and dimensions of expansion chamber 32, and by the rate of flow of the gas as determined by pressure conditions, the rate of gas cooling being affected by changes in each of these elements. 7

Additional control of cooling and, hence, of the percentage of N0 obtained in the process, is obtained by the arrangement as shown in Fig. 2. In this figure the reactor 10 is identical to the showing of Fig. 1, but the cooling equipment is modified by insertion of a pump which cooling liquid may be transmitted and between which the hot gases may flow.

Thesefeatures of importance characterize the apparatus of Figs. 1 and 2, the self-sustaining action of the decomposition which proceeds without need of external heat application, the regenerative heat action wherein the inflowing N 0 gas is preheated by the heated decomposed reversely flowing gases, and the effective control over cooling of the heated gases, whereby the percentage of derived N0 is determined.

In Fig. 3, a modification of the invention is illustrated showing an efficient single pass reactor which may be inserted in the reactor-cooler combination of Fig. l or 2. In this reactor, an elongated main metal tube 46, which may be of steel, is employed, the tube being closed at one end, except for central opening 47, and open at the other end. An inlet pipe 48 has screw-threaded engagement with central opening 47, a valve 49 controlling the fiow of N 0 gas into tube 46.

At the open end of the tube 46 is a stopper 50, this stopper being centrally apertured to form an outlet or orifice 51, an outlet pipe 52, having a control valve 53 therein, being connected, as by screw threads, to an enlarged section of this orifice. A cap 54, with an annular internally threaded depending skirt 55 engages the threaded surface on the outer open end of tube 46, serv- ,ing to forcibly draw the stopper against the open end 'gization of both preheater and initiator coils.

'Figs. 1 and 2.

.second.

of tube 46. Centrally of the cap an opening 56 is formed to provide entry space for the outlet pipe 52.

Tube 46 is divided into two sections: a preheater section 60 and a decomposition chamber section 61. The preheater section 60 consists of metal tube 62, which may be of brass, for example, about which is wrapped a layer of asbestos tape 63, and about the tape a coil is wound of electrical resistance wire, forming a heater 64. One end of the metal tube carries an outer flange and the tube tape heater unit is positioned in the outer tube 46 with the flange edge snugly engaging the inner wall surface thereof adjacent the inlet end.

The decomposition chamber section 61 is placed at the outlet end of tube 46 and includes an open ended cylindrical liner 66 of refractory ceramic or brick abutting the stopper 50 and extending to about one-third the length of the main tube 46. Separating the liner 66 and the end of preheater tube 62 is a barrier unit 67 consisting of two transverse adjoining disks 68 and 69, the disk 68 being of supporting metal and the disk 69 of heat insulating material, such as Transite. As indicated, tthese two disks are formed with multiple alined perforations or apertures 70 for conducting N 0 gas from the preheater section 60 to the decomposition chamber 61. Toward the barrier plates but displaced therefrom is a heater unit which may be termed an initiator 71. This unit is formed of a disk 72 of pressed mica or ceramic about one-quarter inch in thickness, around which is wound an electrically heating wire 73, such as Nichrome, the wire having terminals 74 and being in sections to clear the various perforations 75. It is pointed out that the barrier 67'serves the triple function of separating the preheater and decomposition sections of the reactor, preventing fiash back into the preheating section below and also by means of the multiple apertures 70, directing the preheated N 0 directly against the initiator unit.

'73. The initiator carries the temperature above the decompositionvalue and brings about decomposition of the gas, the liberated heat maintaining the initiator structure at this break down temperature and permitting deener- Thus, the reaction becomes self-sustaining. The decomposed gases escape through outlet orifice 51 into the outlet pipe 52 and. are cooled by either of the methods indicated in In a typical run, chemical analysis indicated the presence of N --56.5%, O -16.8%, NO 15.2% and the balance undecomposed N O-ll.7. For this run, the gas pressure in the reactor was 25.5 atmospheres, the preheat temperature 586 K., the maximum temperature l692 K. and the fiow rate 2.36 grams per It is apparent, however, that their values are subject to considerable variation, the essential conditions being a preheater temperature below the decomposition temperature, the initiator temperature at or above the decomposition temperature, and pressure conditions such as to produce a pronounced flow of the gases. While the apparatus, as above described, is intended primarily for a continuously maintained production of N0 it is apparent that it may be readily applied to any gaseous exothermic compound wherein the heat of decomposition is sufficient to maintain a heat reservoir at or above this heat. a

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A reactor for obtaining self-sustaining exothermic decomposition of a gaseous compound comprising a decomposition chamber, a gas inflow tube connected to said chamber and providing access thereto, supply means connected to said inflow tube for passing a continuous flow of said gaseous compound under pressure through said tube and chamber, heat reservoir means in said chamber located in the path of flow of said gaseous compound under pressure passing from said inflow tube, means located in physical contiguity with said chamber (for initiating said exothermic decomposition and for heating said gasous compound and said heat reservoir means, said heat reservoir means being heated above the decomposition temperature of said gaseous compound by said initial exothermic decomposition whereby said gaseous compound continuously entering said chamber is heated above its temperature of decomposition by said heat reservoir means, an expansion cooling chamber, conduit means interconnecting said decomposition chamber and expansion cooling chamber, an outlet pipe conneeted to said expansion chamber, means for pumping gases from said expansion chamber through said outlet pipe, a return pipe connecting said outlet pipe with said expansion chamber, and a valve positioned in said return pipe for controlling the rate of gas flow therethrough.

2. A reactor for obtaining self-sustaining production of nitrogen dioxide from nitrous oxide comprising a decomposition chamber, a gas inflow tube penetrating one wall 'of said chamber and protruding therein substantially along the longitudinal axis of said chamber extending for more than one-half the length of said chamber and terminating with an open inner end, supply means connected to said inflow tube for passing a continuous flow of said nitrous oxide through said tube and chamber means solely for initiating said exothermic decomposition surrounding said chamber and in contact therewith. heat reservoir means located beyond said open end of said inlet tube with that portion of the chamber located generally between said end of said tube and said heat reservoir means comprising a zone of decomposition, outlet conduit means penetrating a wall of said chamber adjacent the supply end of said inlet tube for removing decomposition products whereby after initiation of said exothermic decomposition in said zone of decomposition with consequent heating of said heat reservoir the nitrous oxide which subsequently continuously enters said chamber via said inlet tube is preheated in said inlet tube by the hot products of decomposition flowing around said tube towards said outlet means whereby after leaving said inlet tube said nitrous oxide is heated above the temperature of decomposition by said heat reservoir, an expansion chamber, conduit means connecting said outlet means with said expansion chamber, on outlet pipe connected to said expansion chamber, means for pump ing cooled gases from said expansion chamber through said outlet pipe, a return pipe connecting said outlet pipe to said expansion chamber, and a valve positioned in said return pipe for controlling the rate of gas flow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 873,891 Pauling Dec. 17, 1907 1,864,541 Hernmann June 28, 1932 2,620,259 McKinnis Dec. 2, 1952 

1. A REACTOR FOR OBTAINING SELF-SUSTAINING EXOTHERMIC DECOMPOSITION OF A GASEOUS COMPOUND COMPRISING A DECOMPOSITION CHAMBER, A GAS INFLOW TUBE CONNECTED TO SAID CHAMBER AND PROVIDING ACCESS THERETO, SUPPLY MEANS CONNECTED TO SAID INFLOW TUBE FOR PASSING A CONTINUOUS FLOW OF SAID GASEOUS COMPOUND UNDER PRESSURE THROUGH SAID TUBE AND CHAMBER, HEAT RESERVOIR MEANS IN SAID CHAMBER LOCATED IN THE PATH OF FLOW OF SAID GASEOUS COMPOUND UNDER PRESSURE PASSING FROM SAID INFLOW TUBE, MEANS LOCATED IN PHYSICAL CONTIGUITY WITH SAID CHAMBER FOR INITIATING SAID EXOTHERMIC DECOMPOSITION AND FOR HEATING SAID GASOUSE COMPOUND AND SAID HEAT RESERVOIR MEANS, SAID HEAT RESERVOIR MEANS BEING HEATED ABOVE THE DECOMPOSITION TEMPERATURE OF SAID GASEOUS COMPOUND BY SAID INITIAL EXOTHERMIC DECOMPOSITION WHEREBY SAID GASEOUS COMPOUND CONTINUOUSLY ENTERING SAID CHAMBER IS HEATED ABOVE ITS TEMPERATURE OF DECOMPOSITION BY SAID HEAT RESERVOIR MEANS, AN EXPANSION COOLING CHAMBER, CONDUIT MEANS INTERCONNECTING SAID DECOMPOSITION CHAMBER AND EXPANSION COOLING CHAMBER, AN OUTLET PIPE CONNECTED TO SAID EXPANSION CHAMBER THROUGH SAID OUTLET GASES FROM SAID EXPANSION CHAMBER THROUGH SAID OUTLET PIPE, A RETURN PIPE CONNECTING SAID OUTLET PIPE WITH SAID EXPANSION CHAMBER, AND A VALVE POSITIONED IN SAID RETURN PIPE FOR CONTROLLING THE RATE OF GAS FLOW THERETHROUGH. 